Nuclear magnetic resonance (NMR) spectroscopy and electron paramagnetic resonance (EPR) are widely used techniques, amongst others, in physical and biological science for structural analysis of compounds. Generally, an aliquot of solution in an elongate precision-made sample tube is placed in a sample chamber located between poles of a powerful magnet and subjected to radio frequency excitation. The sample tube is customarily axially rotated to average out the magnetic field and radio frequency excitation.
Sample tubes for the instruments are frequently made of glass and are available in a plurality of diameters generally ranging from about 0.5 mm to about 16 mm with lengths ranging from about 100 mm to about 8 inches. The most widely used tubes are about 5 mm in diameter and about 7-8 inches long. In use, the tubes are placed in a tube holder that is specifically designed to fit a particular manufacturer's instrument. The tube holder is a precision-made air turbine that spins the sample during the determination of the spectrum.
Since the tubes are elongate and spun during the determination of the spectrum, it is important that the tubes are substantially straight and are substantially coaxial with the tube holder. If the tubes are not substantially straight and coaxial with the tube holder, when the tubes are spun, there will be substantial “run-out” of the bottom portion of the tube that is between the excitation coils and the poles of the magnet. This run-out will degrade the resolution of the spectrum and is very undesirable.
Instrumentation manufacturers supply tube holders to fit specific size tubes. These tube holders, since they are precision-made air turbines, are costly and most users only inventory tube holders for the most commonly used size tubes. In many instances, researchers may only have small amounts of a compound available for testing. In these cases, the standard 5 mm/8 inch tube does not provide a satisfactory vessel for evaluation of these small amounts. As a result, tube manufacturers have developed several sample tubes and adapters to enable use of smaller diameter/low volume samples in standard sample holders.
Laboratory automation systems are frequently used for automated sample preparation and high-throughput screening. Many automated systems require the use of specially shaped tube caps which can be gripped and moved. A particular difficulty with these systems is that the cap can be separated from the sample tube by the autosampler.
Accordingly, there is a need for more universally applicable and simple to use sample tubes capable of being employed in automated sample preparation and analysis systems.